Compression Ratio - Ideas? Anyone Tried.

[Suntzu]

I noticed recently that the CU2 has a 11.5:1 compression ratio. It also revs higher and is still on 95 ron fuel. The CL9 is 10.5 on 95 ron.

My 2005 CL9 has been Jtuned to 98 Ron. I can only use this as the timing etc is advanced and so on. The cars a fair bit quicker than stock and is a lot smoother to drive with better throttle response and the drive by wire delay has been exorcised. Its been really excellent to have the mild tune with my header, CAI and high flow 300 cell cat. It a new car to drive.

Im getting the car dyno'd soon and am hoping for a approx 20kwatw improvement. I did do a baseline but it was stuffed up so i wont have a definative result. I will use the same dyno as Euroact13 though.

On that note Euroact13 i doing an awesome mod fitting a new k20z head to his car, im pretty excited by this. Please see his thread as im not trying to steal his thunder, just making the point that there are other options out there for tuning that are outside the box.

So my question to the gurus here is...

What if I increase my compression ratio to 11.5 like the CU2?

My cars already tuned for 98 ron, it will NEVER have anything less in it so should make good gains and good torque. I understand a 10% increase in compression gives a 10% power torque improvement across the complete rev range.

I have a few questions though:

Would this be done by shaving the head and using a thinner gasket? Is there enough room to do this? Or are we talking expensive pistons here?

Whats the expensive component of this? Removing/installing the head or getting it shaved? What do you think it would cost? Or could i remove it myself given the proper tools and assistance?

What are the associated risks of increasing the compression?

Has anyone done this on other cars with good results?

How do you think it would go in terms of bang for buck?

Maybe i should fit a k20 head AND increase the compression ratio of that at the same time. I wonder if increasing the ratio will screw up my ignition timing or whether it will adapt to the lower head height.

Im after an educated opinion on the potential validity of this idea.

Look forward to your comments.

cheers!

[aaronng]

What happens if you use 95 in your current engine? Will it ping? Because if you just increase your compression without supporting components to reduce pinging, then even 98 RON might be insufficient when you have the reflash and combine it with higher compression.

[Type R Positive]

Yanks have K24 piston kits available.
Costs about US$500 for kit.

Id just swap pistons.

[aaronng]

Yanks have K24 piston kits available.
Costs about US$500 for kit.

Id just swap pistons.

That costs more because you have to pull the block and take out the oil pan, crankshaft, rods and pistons. Might as well build up the k24a using racing pistons, rods and 2.3L crankshaft at the same time! :p

[Type R Positive]

That costs more because you have to pull the block and take out the oil pan, crankshaft, rods and pistons. Might as well build up the k24a using racing pistons, rods and 2.3L crankshaft at the same time! :p
Do you have to go through the bottom to swap pistons?

[aaronng]

Do you have to go through the bottom to swap pistons?

Yup, you need to disconnect the rod from the crankshaft before you can get the piston out through the top. There is no space to remove the pin to remove the piston from the rod while it is still in the block.

[Type R Positive]

Hmmm, I got dirtbikes in my head. Separate cylinder / head / bottom end.....

So, I guess the K20Z head be the go, with benefit from bigger valves and such.
Im not sure how much they cost though.

[Suntzu]

aaronng

so basically you dont think the fact that im only going to use 98 ron fuel would help with ping resistance if I got to say 11.5?

Im not sure who has done this. Im guessing a few of the hybrids k24/k20 have increased the compression. Pistons would be nice but oo bigg a job as you have said.

Might just get a K20 and shave that, that way i can always go back tot the stock head if things go south. I'll wait and see how euroact13 goes.

[aaronng]

aaronng

so basically you dont think the fact that im only going to use 98 ron fuel would help with ping resistance if I got to say 11.5?

Im not sure who has done this. Im guessing a few of the hybrids k24/k20 have increased the compression. Pistons would be nice but oo bigg a job as you have said.

Might just get a K20 and shave that, that way i can always go back tot the stock head if things go south. I'll wait and see how euroact13 goes.

The hybrids use programmable ECUs. So they can run the mixture richer to prevent pinging. Your reflash is fixed, so you will have to work within the constraints of your tuning parameters. Yeah, good idea to see how Eur003act goes with his k20a/k24a hybrid on the stock ECU before committing to a project like this. No doubt the engine will work. But I want to know how it goes with a stock ECU.

[LXRY]

Big bucks either way. Both will have to have the head removed to accomplish. Milling (cutting) the head will result in higher compression BUT it will also result in LESS valve head to piston clearance, POSSIBLY shorter cam drive belt needed, less piston top to cylinder head clearance a lot of work for a street car.

Changing pistons is much easier and the only extra parts used would be the pistons, ring set, piston pin retainer set, and pan gasket and POSSIBLY a rod bearing set. If you assemble the pistons on your work bench the amount of down time will be less (don't have to wait for the machine shop) and all the valve clearance problems should be resolved with the new pistons.

A lot of work for small gains and you might even have to pull some inital timing so you get even less gain that you expected. There are a lot more effective mods that don't involve the expense and work involved that raising your compression ratio.

Installing a shorter final drive would result in more benefit for less time and expense. yes agreed..my old boss always use to say if the motor comes out you have to replace virtualy all componenents gasket's pins
Bearing's etc...

Maybe consider another motor and keep your original one as is just in case shit hits the fan because it can.

[tony1234]

For more get up and go i'd go shorter final drive and lightened flywheel.

[EUR003act]

The hybrids use programmable ECUs. So they can run the mixture richer to prevent pinging. Your reflash is fixed, so you will have to work within the constraints of your tuning parameters. Yeah, good idea to see how Eur003act goes with his k20a/k24a hybrid on the stock ECU before committing to a project like this. No doubt the engine will work. But I want to know how it goes with a stock ECU.

lol i love being the guinea pig :p

lol im more worried about piston 2 valve clearance than anything else... i know the K24A3 is already pretty close, add to that another 1mm of cam lift, and slightly milled head (mirror finish), and i start to sh*t myself... lol

im trying to work out whether to use plasticine, bolt together the enigne, hand crank it a few times, then pull apart and measure... or the easy way of, measure piston to top of block at TDC, then measure top of valve to top of head at VTEC, add them together, and presto, clearance :)

[Suntzu]

Based on my Dyno results yesterday i am confident that my mild reflash as not leaned off to much. Im sitting on about 12.8 flat through the range. That gives me some head room.

That being said all of your comments here have been very revelant and insightful and you have convinced me that this is not a good idea and might be too expensive. I think it would work well but only if money was no object.

i think gains could be made, but im better spending my money on something like Euro03act mods.
Thanks for the advice. Its a learning experince for me at least i have you guys to set me straight.

cheers

[Type R Positive]

Damn Honda....
Bloody expensive for not much gains at all.